Numerous methods and arrangements are known for determining the performance deterioration or the storage capacity of a catalytic converter. These methods and arrangements utilize the signals of oxygen-indicating probes of which one is mounted forward of the catalytic converter and the other rearward thereof. Of special interest with respect to the following are a method and arrangement described in U.S. Pat. No. 3,969,932. The method is carried out on an internal combustion engine having a lambda control for which, in order to make a time measurement, engine speed and load are so adjusted that a pregiven constant flow of gas takes place through the catalytic converter. The engine is then driven in a first operating state having a lambda value of 0.95 or 1.05, that is, a value deviating from one until the catalytic converter in the case of rich operation (that is, the value 0.95) has reached a first storage end state and, in the case of lean operation (that is, the value 1.05) the other storage end state.
For this purpose, a certain time is needed for which it is indicated that it is the time within which the catalytic converter is completely filled with a reducing exhaust gas component or is liberated from this component by oxidation. Actually, a catalytic converter does not store the reducing components but instead stores oxygen. Accordingly, for lean operation, a stored reducing component is not oxidized; rather, oxygen is stored. During rich operation, it is not reducing components which are stored; rather, stored oxygen is consumed by oxidation of reduced components.
After the storage state of the catalytic converter has been transferred in the mentioned first operating state into one of the above-mentioned end positions, that is filled or empty with reference to oxygen, the engine is operated from a start time point in a second operating state with a lambda value deviating from one in the other direction, that is 1.05 or 0.95 whereby the lambda value measured forward of the catalytic converter changes in a corresponding direction and exceeds a threshold at a start time point. The time is measured starting from the start time point and that time point at which the lambda value measured rearward of the catalytic converter runs in the direction of the lambda value present forward of the catalytic converter and thereby exceeds another threshold. This time is a measure for the storage capacity and therefore for the deterioration state of the catalytic converter.
The corresponding arrangement of the invention has an operating state control and a time measuring unit for carrying out the method of the invention.
It is a disadvantage of this method that operating states must be adjusted with well defined air flow and well defined lambda value in order to be able to determine the storage capacity. The method and the arrangement are therefore not useable at any desired steady-state operating states.
Accordingly, the problem was present to provide a method and an arrangement for determining the storage capacity of a catalytic converter which are useable for any desired steady-state operating conditions of the internal combustion engine on which the catalytic converter is operated.